This invention relates to plastic information discs such as digital versatile discs ("DVDs"), compact discs ("CDs"), compact disc read-only memories ("CD ROMs"), and the like, and more particularly to providing an improved aesthetic appearance to surfaces of such light-readable discs.
The information storage capacity of DVDs is large, in part because a DVD comprises two optical discs (each like a CD but with even greater information storage capacity) secured back-to-back (see, for example, U.S. patent application Ser. No. 08/579,302, filed Dec. 27, 1995, the entire contents of which are hereby incorporated by reference herein). The large capacity may be used to record movies and other similar real-time audio/visual programming on discs.
The making of a DVD involves many manufacturing steps during which a surface of the DVD or one of the constituent optical discs can be damaged. For example, a DVD or the constituent optical discs are normally handled with one or more suction devices between manufacturing steps. When a particle, such as a dust particle, is squeezed between an DVD or optical disc surface and the suction device, that surface may be scratched if the suction device moves relative to the disc surface. Also, a suction device may grip the surface of the optical disc before the disc is completely hardened. In that case, the suction device may leave a mark on the surface of the disc where the suction device was in contact with the disc surface. Such defects are especially noticeable when the surface is coated with a reflective material, such as a metal coating, which provides a striking mirror-like finish.
The mirror-like finish may also cause another problem. During manufacture, suction devices repeatedly pick-up and release a disc. However, when the disc surface is smooth, and especially when metallized, the mirror-like surface may make release of the disc more difficult because the suction device cannot vent quickly. Furthermore, the metallized coating may also tend to increase the attractive force that results from a build-up of static electricity.
Still another problem that may adversely affect the appearance of a DVD is unevenness or voids in the adhesive that is used to secure the two optical discs back to back in the DVD. This type of defect tends to be most noticeable near the center of the DVD where no information is recorded and where the constituent optical discs may not be metallized. Thus, such a defect becomes clearly visible through the smooth clear plastic of the constituent optical discs.
In view of the foregoing, it is an object of this invention to provide an improved method of molding an optical disc, especially an optical disc that will be used in a DVD.
It is a more particular object of this invention to provide a method of molding an optical disc so that subsequent handling of that disc is facilitated.
It is yet another object of this invention to provide DVDs that have an improved aesthetic appearance.